S
M
T
W
T
F
S
30
70°
49°
31
69°
50°
1
69°
56°
2
70°
57°
3
75°
57°
4
77°
56°
5
77°
54°
6
72°
48°
7
69°
49°
8
70°
48°
9
69°
46°
10
67°
46°
11
67°
47°
12
69°
46°
13
69°
52°
14
73°
53°
15
67°
47°
16
66°
48°
17
65°
49°
18
64°
51°
19
68°
43°
20
65°
45°
21
66°
43°
22
69°
42°
23
64°
41°
24
63°
42°
25
64°
48°
26
66°
43°
27
64°
48°
28
67°
47°
29
67°
39°
30
61°
43°
1
62°
48°
2
68°
46°
3
66°
40°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Big Boulder
Big Boulder's September 2026 forecast shows daily high temperatures ranging from 61° to 77°, with overnight lows between 39° and 57°. The average high for September is 68° with an average low of 48°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in Big Boulder. See also: October | November | December.
